I appreciate your help, Mkrtich
The old modem, btw, is a TP-Link Archer C7, which isn't all that old. It does support IPv6, and I've always left that in the default, enabled setting.
The printer also supports IPv6, and I've tried that both enabled and disabled. I've also tried it with Bonjour enabled and disabled. Nothing seems to affect my problem. I can hope for a Huawei firmware upgrade, but in the meantime I have to choose between running both modems or running just the Huawei and having to reset it whenever I want to print or scan.
Yes, sometimes printers are annoyingly mysterious, especially in a Windows environment. Sometime ago, I inherited an unwanted old 2007 vintage Brother HL-2170W 802.11 b/g Printer from a business, kept it as a spare for one of my friends in the future, and after reading these posts, thought I should make sure all works before gifting it - had a bit of an adventure with it yesterday. In case it is assistance to anyone, after three hours of experimentation , this is how I got it to work via Wi-Fi using the One Touch method which I had never used before.
1. Did a printer configuration report page. Printer was set to fixed IP 10.0.0.138 on Router 10.0.0.1. Factory Reset Printer by hitting the GO Button seven times - cleared.
2. Downloaded Brother Software. Because the previous owner had used LAN port, I connected a LAN cable, and Added Printer - it came up as Brother HL-2170W series Printer - activated it and then changed the name to Brother HL-2170W Series Printer LAN. All printed and worked fine with IP address 192.168.0.14 being assigned by the Netgear Router (802.11n 2.4Ghz ). Left IP address as unfixed for the test.
3. Whilst connected with LAN cable per install instructions, attempted to set up printer under Brother Wi-Fi Infrastructure mode - Printer Wi-Fi links to Router. Failed.
4. Discovered I could web link into the printer via its IP address 192.168.0.14 and found that its 'Configure Interface' link in Network Configuration screen was set to 10/100 Tx LAN only, so changed that to Auto Mode which enables both LAN and Wireless interfaces to work in whatever mode you are using at the time.
5. Thinking I had discovered the DaVinci code, I then used the One Touch method of linking the Printer to the Modem ; Biro in pin hole for 2 seconds strictly, 3 seconds generates a printout of an 8 digit code which is not used in One Touch. (when you Add Printer, if a Windows screen comes up inviting you to enter 8 digit code, hit Cancel). Printer LEDs indicated it was seeking a WPS connection as a Nominee. Hit the WPS button on the Modem which acts as the WPS Registrar - successful connection. Checked to see if 192.168.0.14 still valid - yes it was.
6. Attempted Print to Brother HL-2170W Series Printer LAN . Failed.
7. Thinking Windows may add a new profile for the Wi-Fi enabled printer, I decided to +Add Printer . This time it came as HL-2170W series Printer - I left it at that to differentiate it from the LAN profile name I had originally assigned.
8. Successful Print through W-Fi! Turned printer OFF and waited five minutes. Turned it back on. Printed OK through Wi-Fi, probably because the DHCP Lease for it had not expired. For practical use, suggest to assign Static IP to Printer.
So, not sure if this applies to other printers, but on this model, you have to firstly enable both the Wireless and LAN ports, then for your printout, select the profile of the printer depending on what connection mode it is in at time of printing. By having different names, it allows you to connect to whatever mode you have working at the time. Thinking I was on a roll, I attempted a USB cable connection but this didn't work - suspect because of the LAN/WLAN setting being in place within the printer prevents the USB port to function. Left it on Wi-Fi setup.